![]() Port prediction techniques are only effective with NAT devices that use known deterministic algorithms for port selection. Techniques that traverse symmetric NATs by attempting to predict the next port to be opened by each NAT device were discovered in 2003 by Yutaka Takeda at Panasonic Communications Research Laboratory and in 2008 by researchers at Waseda University. Hole punching techniques, such as STUN and ICE, fail in traversing symmetric NATs without the help of a relay server, as is practiced in TURN. The recent proliferation of symmetric NATs has reduced NAT traversal success rates in many practical situations, such as for mobile and public WiFi connections. It is claimed that this technique creates more problems than it solves. Application-level gateway (ALG) techniques are a component of a firewall or NAT that provides configureable NAT traversal filters.Socket Secure (SOCKS) is a technology created in the early 1990s that uses proxy servers to relay traffic between networks or systems.NAT hole punching is a general technique that exploits how NATs handle some protocols (for example, UDP, TCP, or ICMP) to allow previously blocked packets through the NAT.Traversal Using Relays around NAT (TURN) is a relay protocol designed specifically for NAT traversal.It was designed for UDP but was also extended to TCP. Session Traversal Utilities for NAT (STUN) is a standardized set of methods and a network protocol for NAT hole punching.It fills in some of the missing pieces and deficiencies that were not mentioned by STUN specification. Interactive Connectivity Establishment (ICE) is a complete protocol for using STUN and/or TURN to do NAT traversal while picking the best network route available.It allows a device on a network to ask the router to open a port. UPnP Internet Gateway Device Protocol (UPnP IGD) is supported by many small NAT gateways in home or small office settings.Port Control Protocol (PCP) is a successor of NAT-PMP.NAT Port Mapping Protocol (NAT-PMP) is a protocol introduced by Apple as an alternative to IGDP.Various NAT traversal techniques have been developed: IETF standards based on this security model are Realm-Specific IP (RSIP) and middlebox communications (MIDCOM). Enterprise security experts prefer techniques that explicitly cooperate with NAT and firewalls, allowing NAT traversal while still enabling marshalling at the NAT to enforce enterprise security policies. NAT traversal techniques usually bypass enterprise security policies. Some methods use the server only when establishing the connection, while others are based on relaying all data through it, which increases the bandwidth requirements and latency, detrimental to real-time voice and video communications. Many traversal techniques require assistance from servers outside of the masqueraded network. As a result, the methods used for NAT traversal are often proprietary and poorly documented. Network address translation technologies are not standardized. Furthermore, many of these types of services carry IP address and port number information in the application data, potentially requiring substitution with deep packet inspection. Incoming requests cannot be easily correlated to the proper internal host. However, applications such as peer-to-peer file sharing, VoIP services, and video game consoles require clients to be servers as well. This is not a problem for general web access and email. This leaves the internal network ill-suited for hosting services, as the NAT device has no automatic method for determining the internal host for which incoming packets from the external network are destined. The network address translator changes the source address in network protocols for outgoing requests from that of an internal device to its external address, so that internal devices can communicate with hosts on the external network, while relaying replies back to the originating device. Network address translation typically uses private IP addresses on private networks with a single public IP address for the router facing the Internet. NAT traversal techniques are required for many network applications, such as peer-to-peer file sharing and voice over IP. ![]() Network address translation traversal is a computer networking technique of establishing and maintaining Internet Protocol connections across gateways that implement network address translation (NAT). Technique for maintaining connection across NAT
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